1. Field of the Invention
The present invention relates to a semiconductor device containing a test circuit which is used to analyze any fault in a wafer state.
2. Description of the Related Art
In the structure of a conventional semiconductor device, external terminals are electrically independent. A voltage which is given to a pair of pads of the external terminals is applied to the internal circuit. FIG. 1 is a circuit diagram which shows a conventional example of a semiconductor circuit. The potential which is given to an external terminal 1 is applied only to an internal circuit 2 which is connected to the external terminal 1. The external terminal 1 is electrically independent from other external terminals.
FIG. 2 is a circuit diagram of a semiconductor device which contains a test circuit which is described in Japanese Laid Open Patent Disclosure (JP-A-Heisei 6-51032). In this circuit, when the test circuit 8 becomes unnecessary, a fuse 4 is cut out so that an input potential is set to a potential which is determined by a depletion type transistor 7. Therefore, the above-mentioned test circuit 8 can be made impossible to operate without applying a potential to an NG terminal 3.
In the above-mentioned conventional example of the semiconductor circuit device shown in FIG. 1, it is sometimes impossible to apply potentials to all external terminals for the reason of physical constraint in a case of the fault analysis of the semiconductor circuit device in a wafer state. In such a case, the external terminal to which any voltage is not applied all is set to a floating state electrically. As a result, there is a problem in that the semiconductor circuit device performs an operation different from an actual operation in the case of the fault analysis in the wafer state.
Also, since the above-mentioned example shown in FIG. 2 has the purpose that only a specific circuit which is not used in the normal state is made impossible to operate, a predetermined external terminal is only set to a predetermined potential. Thus, there is a problem in that an optional external terminal can not be set to an optional potential in accordance with the purpose.